Spurious component reduction

ABSTRACT

A filter includes, in at least one aspect, one or more differential inputs to receive one or more differential input signals, a first filter stage to provide one or more primary poles corresponding to a first frequency associated with the one or more differential input signals, a second filter stage coupled with the first filter stage to provide one or more secondary poles corresponding to a second frequency associated with the one or more differential input signals, the second frequency and the first frequency having a predefined relationship, and one or more differential outputs coupled with the second filter stage to provide one or more differential output signals.

This present disclosure is a divisional of U.S. application Ser. No.12/581,451 (now U.S. Pat. No. 7,957,487), filed on Oct. 19, 2009, whichis a continuation of U.S. application Ser. No. 10/829,801 (now U.S. Pat.No. 7,613,249), filed on Apr. 21, 2004, the disclosures of which areeach incorporated herein by reference in their entireties.

BACKGROUND

The following disclosure relates to electrical circuits and signalprocessing.

A wireless communications transmitter typically converts aninformation-bearing baseband signal from around DC to a high frequencyreferred to as the carrier frequency (e.g., a frequency in the microwaveor RF band) that is suitable for wireless transmission. In many systems,this frequency upconversion process takes place in multiple stages. Thebaseband signal is first upconverted to an intermediate frequency(f_(IF)) that is higher than the bandwidth of the baseband signal. Atthe intermediate frequency, the signal is amplified and filtered beforethe signal is upconverted to the carrier frequency (f_(C)) fortransmission.

In an ideal transmitter, all transmitted signal energy is confined to adedicated frequency channel, and no energy is emitted outside thechannel to interfere with other wireless systems. In practicalrealizations, out-of-band spurious emissions often are generated bytransmitters due to, for example, local-oscillator (LO) harmonics, imagegeneration, and intermodulation.

Spurious emissions caused by the mechanisms mentioned above can fallinto restricted frequency bands and result in an emissions violation.Conventional transceivers can use highly selective external filters(e.g., SAW filters) to suppress undesirable spurious emissions. Externalfilters add to the overall cost and size of the transceiver.

SUMMARY

In one aspect, the invention features an apparatus including a widebandpolyphase filter, which filters an input signal that has an associatedfirst frequency. The wideband polyphase filter has poles correspondingto a first filter frequency and a second filter frequency, where the twofilter frequencies are different. A mixer mixes the filtered signal witha local-oscillator signal at a second frequency to produce anupconverted signal, where the second frequency is substantially aninteger multiple of the first frequency.

In another aspect, the invention features an apparatus including afiltering means, which filters an input signal that has an associatedfirst frequency. The filtering means has poles corresponding to a firstfilter frequency and a second filter frequency, where the two filterfrequencies are different. A mixing means mixes the filtered signal witha local-oscillator signal at a second frequency to produce anupconverted signal, where the second frequency is substantially aninteger multiple of the first frequency.

In one aspect, the invention features a wireless transceiver thatincludes a transmitter to transmit a modulated carrier signal. Thetransmitter includes a communications circuit, where the communicationscircuit includes a wideband polyphase filter that filters an inputsignal. The input signal has an associated first frequency, and thewideband polyphase filter has poles corresponding to a first filterfrequency and a second filter frequency, where the two filterfrequencies are different. The communications circuit also includes amixer that mixes the filtered signal with a local-oscillator signal at asecond frequency to produce an upconverted signal, where the secondfrequency is substantially an integer multiple of the first frequency.

In another aspect, the invention features a wireless transceiver thatincludes a transmitting means to transmit a modulated carrier signal.The transmitting means includes an upconversion means, where theupconversion means includes a filtering means that filters an inputsignal. The input signal has an associated first frequency, and thefiltering means has poles corresponding to a first filter frequency anda second filter frequency, where the two filter frequencies aredifferent. The upconversion means also includes a mixing means thatmixes the filtered signal with a local-oscillator signal at a secondfrequency to produce an upconverted signal, where the second frequencyis substantially an integer multiple of the first frequency.

In yet another aspect, the invention features a process for reducingspurious components in an upconverted signal, where the process includesfiltering an input signal that has an associated first frequency toproduce an in-phase filtered signal and a quadrature filtered signal.The quadrature filtered signal is substantially ninety degrees out ofphase with the in-phase filtered signal at first and second filterfrequencies, where the two filter frequencies are different. Thein-phase filtered signal is mixed to a second frequency to produce anin-phase upconverted signal, where the second frequency is substantiallyan integer multiple of the first frequency. The quadrature filteredsignal is also mixed to the second frequency to produce a quadratureupconverted signal.

Particular implementations may include one or more of the followingfeatures. The first frequency can correspond to a fundamental frequencyof an intermediate-frequency local-oscillator signal. The first filterfrequency can correspond to a desired signal in the input signal, andthe second filter frequency can correspond to a spurious component inthe input signal. The first filter frequency can be substantially equalto the first frequency, and the second filter frequency can be anon-unity integer multiple of the first frequency.

The filtered signal can include an in-phase component and a quadraturecomponent, the local-oscillator signal can include an in-phase componentand a quadrature component, and the upconverted signal can include anin-phase component and a quadrature component. The mixer can mix thein-phase component of the filtered signal with the in-phase component ofthe local-oscillator signal to produce the in-phase component of theupconverted signal and mix the quadrature component of the filteredsignal with the quadrature component of the local-oscillator signal toproduce the quadrature component of the upconverted signal. A circuitcan combine the quadrature component of the upconverted signal and thein-phase component of the upconverted signal to produce an outputsignal.

The apparatus, system, or method can be compliant with any of IEEEstandards 802.11, 802.11a, 802.11b, 802.11g, 802.11i, 802.11n, and802.16.

In one aspect, the invention also features a wideband polyphase filterthat has one or more poles corresponding to a first frequency and one ormore poles corresponding to a second frequency, where the secondfrequency is different than the first frequency. The first frequency cancorrespond to a fundamental frequency of an intermediate-frequencylocal-oscillator signal, and the second frequency can correspond to afrequency of a spurious component.

In another aspect, the invention features a process for reducingspurious components in an upconverted signal. The process includes firstmixing an input signal to a first frequency, thereby producing anintermediate signal. The intermediate signal is mixed to a secondfrequency, thereby producing an upconverted signal, where the secondfrequency is different than the first frequency. The first frequency andthe second frequency are selected such that a spurious component of theintermediate signal generated in the first mixing falls, whenupconverted, on a same frequency as another component in the upconvertedsignal. The second frequency can be selected to be an integer multipleof the first frequency.

Implementations can include one or more of the following advantages. Amethod, apparatus, and system are disclosed that can be used to reduce anumber of spurious components in an output signal of a transmitter.Intermodulation products typically will overlap existing spuriouscomponents instead of creating new spurious components. The method,apparatus, and system can also attenuate spurious components in theoutput signal. The method, apparatus, and system can substantiallyremove critical spurious components from the output signal usinginternal filters and can reduce the cost and/or size of a communicationstransmitter or receiver.

These general and specific aspects may be implemented using anapparatus, a system, a method, or any combination of apparatus, systems,and methods.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features andadvantages will become apparent from the description, the drawings, andthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a system for upconverting a signal.

FIG. 1B is a graph of signals generated by mixing a baseband signal withan upconversion signal.

FIG. 2 is a schematic of a polyphase filter circuit.

FIG. 3 is a block diagram of a system for upconverting a signal whilereducing spurious components.

FIG. 4 is a graph of the phase difference between the in-phase andquadrature outputs of a polyphase filter.

FIG. 5 is a flowchart of a process to reduce spurious components in atransmitter.

FIG. 6 is a block diagram of a wireless transceiver.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1A is a block diagram of a conventional system 100 that can be usedto convert a baseband signal to a radio-frequency (RF) signal. Anin-phase component of the baseband signal is applied to a terminal 104,and a quadrature component of the baseband signal is applied to aterminal 106. A mixer 120 mixes the in-phase component of the basebandsignal with an LO signal at an intermediate frequency from a signalsource 110 to create an in-phase intermediate-frequency (IF) signal 122.A mixer 125 mixes the quadrature component of the baseband signal withan LO signal at the intermediate frequency from a signal source 115 tocreate a quadrature IF signal 124. The LO signal from signal source 115is at a same frequency as the LO signal from signal source 110, but isshifted in phase by ninety degrees. For example, the LO signal fromsignal source 110 can be of the form of a cosine wave at intermediatefrequency f_(IF) and the LO signal from signal source 115 can be of theform of a sine wave at f_(IF). Mixers 120 and 125 will hereafter bereferred to collectively as the first mixer, the in-phase and quadraturecomponents of the baseband signal will be referred to collectively asthe baseband signal, and the LO signals from signal sources 110 and 115will be referred to collectively as the first LO signal unless otherwisenoted.

The first mixer can generate spurious components (e.g., due to clockharmonics) when mixing the baseband signal with the first LO signal.Because the mixer function is approximately a square wave, the outputsignal will have a fundamental frequency component at the intermediatefrequency and harmonics at odd integer multiples of the intermediatefrequency. Referring to FIG. 1B, a frequency spectrum 105 represents themagnitude signals at the output of the first mixer. Frequency spectrum105 includes a desired signal 172 at the intermediate frequency.Frequency spectrum 105 also includes copies 174-178 at odd harmonics ofthe intermediate frequency. Copies 174-178 are spurious components,since only desired signal 172 is desired to be transmitted. In someimplementations, a signal at a frequency other than the fundamentalfrequency of the first LO signal may be the desired signal.

Referring again to FIG. 1A, the in-phase 122 and quadrature 124 IFsignals are combined by an adder 130. Depending on the implementationused, adder 130 can add the in-phase and quadrature IF signals orsubtract one of the IF signals from the other. A combined IF signal 132is filtered by a highly selective bandpass filter 135 (e.g., an externalSAW filter). Filter 135 reduces spurious components due to LO harmonicsand leaves the desired component at the intermediate frequency. Afiltered IF signal 137 from filter 135 is provided to a polyphase filter140.

FIG. 2 illustrates a filter circuit 200 that can be used to implementpolyphase filter 140 (FIG. 1A). Filter circuit 200 has differentialinputs 210 and 220, differential outputs 230 and 240, and differentialoutputs 250 and 260. Filter circuit 200 is constructed by cascadingseveral stages of RC-CR networks (stages 270, 280, and 290). Each ofstages 270, 280, and 290 has an RC time constant corresponding to a poleof filter circuit 200. At each pole frequency of filter circuit 200, theamplitude of the output signal at differential outputs 230 and 240 isthe same as the amplitude of the output signal at differential outputs250 and 260, but the phases of the output signals are separated byninety degrees. The pole frequencies of filter circuit 200 typically areplaced close to the IF frequency of system 100 (FIG. 1A) to providematching amplitudes and an accurate ninety degree phase separation atthe intermediate frequency even when process variations occur in the Rand C values of stages 270, 280, and 290. Typically, at frequencies awayfrom the intermediate frequency the amplitudes of the output signalswill not be matched or the phase difference between the output signalswill deviate from ninety degrees (depending on whether the polyphasefilter is driven by a current or by a voltage). A conventionalimplementation of a polyphase filter is therefore a narrowband structureexhibiting a ninety-degree phase separation over a relatively narrowrange of frequencies.

Referring again to FIG. 1A, polyphase filter 140 outputs two signals atthe intermediate frequency—one in-phase filtered signal 142 and onequadrature filtered signal 144. The quadrature filtered signal 144 issubstantially ninety degrees out of phase with the in-phase filteredsignal 142 at frequencies corresponding to the poles of the polyphasefilter 140. The filtered signals (142, 144) from the output of polyphasefilter 140 are converted to RF signals by a mixer 160 and a mixer 165.Mixer 160 mixes the in-phase filtered signal 142 with an LO signal froma signal source 150 to create an in-phase signal 162. Mixer 165 mixesthe quadrature filtered signal with an LO signal from a signal source155 to create a quadrature signal 164. The LO signals from signalsources 150 and 155 have the same frequency (f_(RF)), but the signalfrom signal source 155 is shifted in phase by ninety degrees relative tothe signal from signal source 150. For example, the LO signal fromsignal source 150 can be of the form of a cosine wave at f_(RF), and themixer signal from signal source 155 can be of the form of a sine wave atf_(RF). Mixers 160 and 165 will hereafter be referred to collectively asthe second mixer, and the LO signals from signal sources 150 and 155will be referred to collectively as the second LO signal.

Signals 162 and 164 each contain two components—a desirable component atthe carrier frequency f_(C)=f_(RF)+f_(IF), and an image atf_(RF)−f_(IF). Because of the phase shifts between signals 142 and 144and between the signals from signal sources 150 and 155, the desirablecomponents of signals 162 and 164 are out of phase with each other, andthe image components of signals 162 and 164 are in phase with eachother. When signal 164 is subtracted from signal 162 to produce anoutput signal 170, the image components cancel and only the desirablecomponent at the carrier frequency is left. Polyphase filter 140, mixer160, and mixer 165 form an image-rejection mixer structure.

System 100 relies on filter 135 to remove spurious components due to LOharmonics. If the spurious components are not filtered by filter 135,they can pass through the image-rejection mixer structure and reachoutput signal 170. In addition, because the narrow-band polyphase filter140 typically does not produce ninety degree phase separation or matchedamplitudes at the spurious component frequencies, images of the spuriouscomponents are not cancelled by the image-rejection mixer structure,resulting in spurious components in output signal 170.

FIG. 3 illustrates a system 300 that can be used to substantially reducespurious emissions without relying on an external filter. System 300significantly reduces the number of spurious components and canselectively remove spurious components that would otherwise fall intoundesirable frequency bands (e.g., restricted bands). Referring to FIG.1A and FIG. 3, system 300 is similar to system 100, but has someimportant differences. For example, filter 135 (e.g., an externalhigh-selectivity bandpass filter) is replaced by an optional internalfilter 335. Filter 335 mildly attenuates spurious components due to LOharmonics and can be, for example, a low-selectivity low-pass filter.

In system 100, the intermediate frequency (f_(IF)) and the frequency ofthe second LO signal (f_(RF)) can be chosen independently of each other,except that the sum of the intermediate frequency and the frequency ofthe second LO signal should be equal to the desired channel frequency(f_(C)). The requirement that f_(IF)+f_(RF)=f_(C) assumes that system100 uses high-side mixing, where f_(IF) is lower than f_(C). If system100 uses low-side mixing (where f_(IF) is higher than f_(C)), thedifference between the intermediate frequency and the frequency of thesecond LO signal should be equal to f_(C). If the spurious componentsdue to LO harmonics were not removed by filter 135, all of the spuriouscomponents and the associated images generated in the second mixer wouldtypically fall on distinct frequencies, resulting in a large number ofspurious components in output signal 170.

In one implementation of system 300, a fixed integer-ratio relation(hereafter referred to as a ratio-based LO frequency plan) between thefrequencies of the second and first LO signals (f_(RF) and f_(IF)) isimposed (i.e., f_(RF)=K*f_(IF), and f_(C)=f_(RF)+f_(IF)=(K+1)f_(IF),where K is a positive integer). The fixed integer-ratio reduces thenumber of spurious components. When there is a fixed integer-ratiorelating f_(RF) to f_(IF), a spurious component in the output signal 370due to the N^(th) LO harmonic in the first mixer (at frequencyf_(RF)+N*f_(IF)=(K+N)*f_(IF)) will overlap an image generated in thesecond mixer due to the M^(th) LO harmonic of the first mixer (atfrequency |fRF−M*f_(IF)|=|K−M|*f_(IF)) whenever K+N=|K−M|. The totalnumber of spurious components in output signal 370 therefore can bereduced.

The constant ratio K is typically chosen to be a power of two (i.e., 1,2, 4, . . . ) so that the first LO signal can be generated by dividingdown the second LO signal. Therefore, only a single local oscillator isneeded in system 300. Two factors to consider when choosing the value ofK are the number of spurious components (which decreases with decreasingK) and whether the resulting frequency plan will generate spuriouscomponents in undesirable frequency bands.

System 300 includes a wideband polyphase filter 340, which selectivelyattenuates critical spurious components. A conventional implementationof a polyphase filter, as described in the context of FIG. 2, involvescascading several RC-CR networks with pole frequencies that are close toa single frequency. A wideband polyphase filter includes one or moreadditional RC-CR sections with poles away from the primary polelocation. By placing one or more secondary poles at frequencies ofcritical spurious components, the amplitude matching and phase splittingproperties of the polyphase filter can function at one or more spuriouscomponent frequencies, which sharply attenuates corresponding spuriouscomponent images in output signal 370. FIG. 4 shows the phase responseof wideband polyphase filter 340.

In principle, any spurious component image that is located at afrequency lower than the carrier frequency can be removed in a high-sidemixing system using the ratio-based LO frequency plan (discussed abovein reference to system 300) by strategically placing a secondary pole inthe wideband polyphase filter. For example, if an LO frequency ratio Kof four is chosen, f_(IF)=2.4 GHz/5=480 MHz, f_(RF)4*f_(IF)=1.92 GHz,the desired output signal is at 2.4 GHz (=f_(RF)+f_(IF)), and spuriouscomponents can occur at frequencies N*480 MHz, where N is any integer.If the spurious component located at 3*480 MHz=1.44 GHz falls in arestricted band, the spurious component should be maximally attenuated.The spurious component at 1.44 GHz originates from two sources: an imageof the desired signal generated in the second mixer (since|f_(RF)−f_(IF)|=4−1|*480 MHZ=1.44 GHz), and an image generated in thesecond mixer due to the 7^(th) LO harmonic of the first mixer (since|f_(RF)−7*f_(IF)|=|4−7|*480 MHz=1.44 GHz). The former image is rejectedby the image-rejection mixer structure, since the primary poles ofwideband polyphase filter 340 are placed around f_(IF). The latter imagecan be attenuated if a secondary pole of wideband polyphase filter 340is placed at the frequency of the 7^(th) LO harmonic (3.36 GHz).

Referring to FIG. 5, a process is shown whereby a baseband signal can beconverted to an RF signal. A baseband signal is mixed with an LO signalat an intermediate frequency f_(IF) (step 510) to produce an IF signal.The IF signal may contain spurious components at integer multiples off_(IF). The IF signal is filtered with a wideband polyphase filter (step520). The wideband polyphase filter has at least one pole at theintermediate frequency and at least one pole at a frequency thatcorresponds to a spurious component. The wideband polyphase filteroutputs an in-phase filtered signal and a quadrature filtered signal.The quadrature filtered signal is substantially ninety degrees out ofphase from the in-phase filtered signal at the intermediate frequencyand at the frequency of the pole corresponding to the spuriouscomponent.

In step 530, an in-phase signal is produced by mixing the in-phasefiltered signal with an in-phase LO signal at a radio frequency that isan integer multiple of the intermediate frequency. A quadrature signalis produced by mixing the quadrature filtered signal with a quadratureLO signal at the radio frequency, where the quadrature LO signal issubstantially ninety degrees out of phase with the in-phase LO signal.

The quadrature signal produced in step 530 is combined with the in-phasesignal produced in step 530 (step 540). For example, the quadraturesignal can be subtracted from the in-phase signal. The combining removesimages from the resulting signal that correspond to the frequencies inthe IF signal at which poles are located. For example, if one or morepoles of the wideband polyphase filter are located at the intermediatefrequency and one or more poles are located at seven times theintermediate frequency when the radio frequency is four times theintermediate frequency, the images in the signal output from step 540 atthree times the intermediate frequency will be removed. The image atthree times the intermediate frequency can be removed by placing a poleat the intermediate frequency, and the other image that falls on threetimes the intermediate frequency can be removed by placing a pole atseven times the intermediate frequency.

The described spurious component reduction system and method can be usedin a wide range of applications. Referring to FIG. 6, the system andmethod can be used in a wireless transceiver 600 (hereafter referred toas transceiver 600). The transmit path of transceiver 600 includesdigital-to-analog converters (DACs) 605 and 606 that supply in-phase andquadrature components of a baseband signal to a mixer 120 and a mixer125 respectively. Mixer 120 modulates a signal generated by a signalsource 610 with the in-phase baseband signal and mixer 125 modulates asignal generated by a signal source 615 with the quadrature basebandsignal, where the signal generated by signal source 615 is substantiallyninety degrees out of phase with the signal generated by signal source610 and at the same frequency (the intermediate frequency). The in-phaseand quadrature modulated signals are combined in an adder 130 and thecombined signal is optionally filtered by a lowpass filter 335 toattenuate spurious components in the combined signal.

The filtered signal is filtered by a wideband polyphase filter 340 toproduce an in-phase filtered signal and a quadrature filtered signal.Wideband polyphase filter 340 has poles corresponding to the frequencyof the signal generated by signal source 610 and corresponding to thefrequency of a spurious component in the filtered signal. A mixer 160modulates the in-phase filtered signal with a signal generated by asignal source 650 to produce an in-phase RF signal. A mixer 165modulates the quadrature filtered signal with a signal generated by asignal source 655 to produce a quadrature RF signal. The signalgenerated by signal source 655 is substantially ninety degrees out ofphase with the signal generated by signal source 650. In oneimplementation, the signals generated by signal sources 650 and 655 areboth at a frequency that is an integer multiple of the intermediatefrequency. An adder 170 subtracts the quadrature RF signal from thein-phase RF signal to attenuate images in the RF signal. An amplifier620 amplifies the RF signal and transmits the RF signal using an antenna630.

The receive path of transceiver 600 includes a receiver 640 and ananalog-to-digital converter 645. Transceiver 600 can be IEEE 802compliant with the following standards: 802.11, 802.11a, 802.11b,802.11g, 802.11i, 802.11n, and 802.16.

This application describes a method, apparatus, and system that can beused to reduce spurious emission from a transmitter without relying onexternal filters. The method, apparatus, and system can include one orboth of the following aspects: first, a ratio-based LO frequency plancan be used to reduce the total number of spurious components generated;second, a wide-band polyphase filter can be employed to selectivelyremove critical spurious components around the carrier frequency.Various implementations have been described. These and otherimplementations are within the scope of the following claims. Forexample, the method, apparatus, and system described above can be usedwith different transceiver architectures. The polyphase filter in themethod, apparatus, and system can also include multiple poles atmultiple frequencies corresponding to multiple spurious components.

What is claimed is:
 1. A filter comprising: one or more differentialinputs to receive one or more differential input signals; a first filterstage to provide one or more primary poles corresponding to a firstfrequency associated with the one or more differential input signals; asecond filter stage coupled with the first filter stage to provide oneor more secondary poles corresponding to a second frequency associatedwith the one or more differential input signals, the second frequencyand the first frequency having a predefined relationship; and one ormore differential outputs coupled with the second filter stage toprovide one or more differential output signals.
 2. The filter of claim1, wherein the one or more primary poles of the first filter stage areplaced with respect to the first frequency to provide matchingamplitudes and phase separation at the first frequency; and wherein theone or more secondary poles of the second filter stage are positionedapart from the one or more primary poles.
 3. The filter of claim 1,wherein the predefined relationship includes a ratio-based relationshipdefining a ratio between the first frequency and the second frequency.4. The filter of claim 3, wherein the ratio defines a frequency value ofthe second frequency as a power of two of the first frequency.
 5. Thefilter of claim 1, wherein at least one primary pole corresponds to afirst component in the one or more differential input signals; andwherein at least one secondary pole corresponds to a second component inthe one or more differential input signals.
 6. The filter of claim 1,wherein the first filter stage filters out a first image componentassociated with the one or more differential input signals at the firstfrequency; and wherein the second filter stage filters out a secondimage component associated with the one or more differential inputsignals at the second frequency.
 7. The filter of claim 1, wherein theone or more differential output signals include an in-phase filteredsignal and a quadrature filtered signal; and wherein the in-phasefiltered signal and the quadrature filtered signal are out of phase fromeach other at the first frequency and the second frequency.
 8. A methodcomprising: receiving one or more differential input signals; filteringin accordance with one or more primary poles corresponding to a firstfrequency associated with the one or more differential input signals;filtering in accordance with one or more secondary poles correspondingto a second frequency associated with the one or more differential inputsignals, the second frequency and the first frequency having apredefined relationship; and generating one or more differential outputsignals based on the predefined relationship.
 9. The method of claim 8,wherein: filtering in accordance with the one or more primary polesincludes filtering in accordance with the one or more primary poles withrespect to the first frequency to provide matching amplitudes and phaseseparation at the first frequency; and filtering in accordance with theone or more secondary poles includes positioning the one or moresecondary poles apart from the one or more primary poles.
 10. The methodof claim 8, further comprising establishing the predefined relationshipas a ratio-based relationship that defines a ratio between the firstfrequency and the second frequency.
 11. The method of claim 10, whereinestablishing the predefined relationship includes setting the ratio todefine a frequency value of the second frequency as a power of two ofthe first frequency.
 12. The method of claim 8, wherein: filtering inaccordance with one or more primary poles includes filtering inaccordance with at least one primary pole that corresponds to a firstcomponent in the one or more differential input signals; and filteringin accordance with one or more secondary poles includes filtering inaccordance with at least one secondary pole that corresponds to a secondcomponent in the one or more differential input signals.
 13. The methodof claim 8, wherein: filtering in accordance with one or more primarypoles includes filtering out a first image component associated with theone or more differential input signals at the first frequency; andfiltering in accordance with one or more secondary poles includesfiltering out a second image component associated with the one or moredifferential input signals at the second frequency.
 14. The method ofclaim 8, wherein: generating the one or more differential output signalsinclude generating an in-phase filtered signal and a quadrature filteredsignal, the in-phase filtered signal and the quadrature filtered signalbeing out of phase from each other at the first frequency and the secondfrequency.
 15. A method comprising: receiving an intermediate frequencysignal; filtering the intermediate frequency signal in accordance withone or more first poles at an intermediate frequency of the intermediatefrequency signal and one or more second poles at a frequencycorresponding to a second component of the intermediate frequency signalto produce a filtered signal; and generating a filtered intermediatefrequency signal to be mixed with a predetermined frequency to providean output signal, the predetermined frequency being an integer multipleof the intermediate frequency.
 16. The method of claim 15, whereinfiltering the intermediate frequency signal includes filtering theintermediate frequency signal based on a ratio-based relationship withrespect to the predetermined frequency to allow the second componentassociated with the intermediate frequency signal to fall on a samefrequency as an image component in the output signal.
 17. The method ofclaim 15, wherein filtering the intermediate frequency signal includesfiltering the intermediate frequency signal in accordance with aratio-based frequency plan to reduce a number of spurious componentspresent in the received intermediate frequency signal and the outputsignal.
 18. The method of claim 15, wherein filtering the intermediatefrequency signal includes: selecting the intermediate frequency and thepredetermined frequency independently of each other; and filtering theintermediate frequency signal based on the selected intermediatefrequency.
 19. The method of claim 15, wherein filtering theintermediate frequency signal includes: selecting the intermediatefrequency and the predetermined frequency such that a sum of theintermediate frequency and the predetermined frequency is equal to adesired channel frequency; and filtering the intermediate frequencysignal based on the selected intermediate frequency.
 20. The method ofclaim 19, wherein receiving the intermediate frequency signal includesreceiving the intermediate frequency signal generated from a basebandsignal having mixed with the intermediate frequency, the intermediatefrequency lower than the desired channel frequency.